This invention pertains to an opthalmic surgical device and to methods for performing corrective refractive surgery on eyes. One of the first procedures for refractive surgery was the Barraquer microkeratome which placed against the cornea a flat applanate surface supported with the knife (as in a plane) guided by spaced apart dovetailed guides which formed rails on a suction ring applied to the sclera and then manually passed across the cornea at an angle thereto a power driven reciprocating knife edge in a guideway to remove a round lamellar (sides parallel to the surface of the cornea) disk. The thickness of the cut disk was controlled by the thickness of a spacer plate (numerous plates for various thicknesses) and the cut disk rolled up into a groove between the spacer plate and the block carrying the knife as the cut was made. The cut disk was then frozen, lathed and replaced. The procedure was known as keratomileusis.
Mechanical devices known as keratomes have been utilized to perform multiple lamellar cuts of the cornea. In this procedure, a first disk is cut. Then a second smaller disk is cut and removed. The first disk is sewn back on. This procedure, known as keratomileusis in-situ, eliminated the freezing process and overcame many of the problems of the keratomileusis procedure. However, keratomes still lacked precision, predictability and the ability to make smooth corneal cuts.
Microkeratomes, for example, Giraud et al U.S. Pat. No. 5,288,292, applicant being a co-inventor thereof, have replaced Barraquer's multiple spacer plates for controlling the thickness of the cut with a single adjustable plate which controls the space between the plate and knife edge and, hence, the slice thickness. Micrometers have been placed on the microkeratome to precisely control the thickness.
The procedure known as radial keratotomy is used extensively for the correction of low to medium myopia and astigmatism. The procedure involves changing the shape of the cornea by making deep corneal cuts which are 80-90% of corneal thickness extending out from a central optical zone of about 3 mm diameter. While many patients report satisfactory results, others are bothered by regression and many experience a starburst effect from the reflection of light at nighttime when the pupil is dilated larger than 3 mm. The scars from the deep corneal incisions scatter light at night time. Radial keratotomy is usually limited to about 8 diopters of refractive correction.
Eximer lasers have been used for corneal sculpturing for correction of myopia and astigmatism. The eximer laser ablates (removes by vaporization) the cornea in a manner that results in removing a lenticular (sides not parallel to the surface of the cornea) disk from the cornea with a diameter of about 5-6 mm. The procedure requires that the epithelium (thin outer layer of the eye) be scraped off. Then the eximer laser ablates the cornea in a series of stepped ablations which leave a less than smooth surface on the corneal bed. The procedure subjects patients to substantial pain for a few days and obstructed vision for months. The use of eximer lasers to remove superficial irregularities of the cornea has met with mixed success due to ablation induced hyperopic shifts of corneal refraction.
U.S. Pat. No. 4,662,370 shows a device in which the adjustable movable plate of the earlier devices has been replaced by a fixed plate. This device begins the cut of the cornea outside of the correction zone, passing superstructure over the cornea blocking the surgeons view during the cut, and requires the complexity and cost of multiple vacuums chambers.
There remains a long felt need for a smooth cutting keratome that can be used for all defective vision corrections including those requiring irregular cuts, cuts only under a prescribed, predetermined corrected surface and which provides automated advance without blocking the surgeon's vision during the cut.